Preheat the oven to 400˚F. Line a small baking sheet (such as a ¼ baking sheet) with foil. Toss the halved tomatoes in the olive oil, and spread on the sheet. Lightly salt and pepper. Roast for 15 minutes, or until they're soft, and starting to crisp around the edges. Leave the oven on for baking the casserole.

Bring a shallow pan of well-salted water to a boil over high heat. Add the beans, and cook for 5 - 7 minutes to blanch. Drain and run cold water over the beans. Wipe out the pan, and return it to the stove.

Melt the butter in the pan over medium heat, and add the shallots. Sauté for 10 minutes, stirring occasionally, until the shallots are fragrant and starting to brown. Sprinkle the flour over the tops of the shallots. Toss the shallots to completely coat them, and cook for 5 - 10 minutes, moving the shallots around the pan occasionally. The flour should begin to lightly brown.

Reduce the heat to medium-low, and gradually add the broth, constantly stirring with a whisk. Once the broth is completely absorbed into the flour and shallots, gradually add the half and half, and continue to whisk until a sauce forms. Add the salt and pepper, and cook for 5 - 10 minutes on a very low simmer to thicken the sauce. Reduce the heat if necessary, and stir occasionally to prevent the sauce from sticking to the bottom of the pan.

Remove from the heat. Stir in the cheese using a large wooden spoon. Once it's completely melted, add the roasted tomatoes and beans. Gently toss to completely coat the vegetables with the sauce. Pour into a well-buttered baking dish and top with the Crispy Fried Onions.

Bake for 20 minutes, or until bubbly and the topping is browned.